Characterization of Corrosion Interfaces by the Scanning Kelvin Probe Force Microscopy Technique

Abstract

A variety of interfaces relevant to corrosion processes were examined by the scanning Kelvin probe force microscopy (SKPFM) technique in order to study the influences of various parameters on the measured potential. SKPFM measurements performed on AA2024-T3 after solution exposure showed that surface composition is not the only parameter that controls the Volta potential difference, which is measured by SKPFM. The influence of surface oxide structure and adsorption at the oxide surface can be probed by SKPFM and lateral potential gradients can be observed in the absence of significant differences in oxide composition. The influence of tip-sample separation distance on the measured Volta potential difference was studied for different pure oxide-covered metals. SKPFM measurements were made in air on pure Ni and Pt samples withdrawn from solution at open circuit or under potential control. The Volta potential difference was found to be composed of a transient component that slowly discharged and a more permanent component associated with the charge of adsorbed species. The Volta potential difference transients measured on the samples emersed under potential control decayed much slower than the open-circuit potential transient measured in solution upon release of the potential control. These different measurements validate the use of SKPFM for the prediction of local corrosion sites and the study of surface modification during solution exposure